Author
 |
Robertson, Nancy |
|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 12/8/2011 Publication Date: 3/20/2012 Citation: Robertson, N.L. 2012. First report of apple mosaic virus in Alaska. Plant Disease. 96(3):463. Interpretive Summary: Apple mosaic virus (ApMV) is a plant pathogen that infects apples and at least 65 other plants around the world. It may cause from zero to fifty percent yield reduction in apples. Although home gardeners in Alaska have raised hardy cold tolerant apples for approximately 100 years, little attention has been given to the detection and documentation of viruses in fruit trees. In July 2011, during a survey for pathogens in an apple orchard of 118 trees, bright yellow mosaic leaves were observed on one apple tree, cultivar ‘Valentine’ in Wasilla, Alaska. Leaves were collected from all the trees and assayed by molecular techniques and serology to identify the pathogen. The results showed that two trees, cultivars ‘Valentine’ and ‘Geneva Early’ were infected with ApMV, with only the former having pronounced leaf discolorations. Movement of ApMV from plant to plant is mainly by using infected propagated plant material. This finding of ApMV in Alaska is important to growers in the state in that sources of rootstocks and grafting material should be indexed for viruses before distribution, and to avoid grafting virus infected material. Technical Abstract: Apple mosaic virus (ApMV, family Bromoviridae, genus Ilarvirus) is one of the oldest and most economically important viruses of apples (Malus x domestica Borkh.). Yield losses may vary from negligible to as high as fifty percent, depending on the affected cultivar. Although ApMV is found worldwide and occurs naturally in over 65 plant species, it has not been reported to occur in Alaska. In July 2011, noticeably bright yellow mosaic leaves were observed on the apple cultivar ‘Valentine’ and its rootstalk ‘Ranetka’ from an apple orchard in Wasilla, Alaska. Leaves were collected and assayed by reverse transcription (RT)-PCR using ApMV specific primers and total RNA extracted with buffer modifications to RNeasy plant mini kit (Qiagen,Valencia, CA). Direct sequencing of the predicted ~ 260 bp PCR product resulted in 97% to 98% nucleotide identities to ApMV accessions in GeneBank when analyzed by BLAST. In order to determine the distribution and incidence of infection in the Wasilla orchard, all 118 apple trees (99 cultivars) were then sampled and assayed serologically by double-antibody sandwich-ELISA with ApMV antiserum according to manufacturer’s protocol (Agdia, Inc., Elkhart, IN). Apple cultivar ‘Geneva Early’ and the same ‘Valentine’ tree and its rootstock tested positive for ApMV by ELISA and RT-PCR. Strong diagnostic ApMV symptoms were not apparent on the infected ‘Geneva Early’, which is typical for most commercially grown apples. An additional twenty-one apple trees with no symptoms from an orchard in Talkeetna tested negative to ApMV by ELISA. Limited natural spread of ApMV to other plants may be by pollen and seed transmission. The most prevalent mode of transmission is from ApMV infected rootstock and grafts. It is important to obtain new propagation plant material from certified virus tested nurseries and to avoid grafting plant material containing ApMV. |
